The present invention relates to a method of adhering a wafer and a wafer adhering device, more precisely relates to a method of adhering a wafer onto a preheated carrier plate before abrading the wafer and a wafer adhering device for executing said method.
Generally, in the case of abrading or polishing a wafer, one side face of the wafer is adhered onto a flat face of a tough carrier plate, and the other side wafer held by the carrier plate is abraded or polished.
Wafers are thin and apt to warp, so it is difficult to maintain wafers flat. But flatness of the wafers adhered can be maintained by the tough carrier plate, so that the wafers can be abraded easily.
To abrade or polish the faces of the wafers with high flatness, the wafers must be precisely adhered onto the carrier plate, and flatness of the carrier plate must be high.
Especially, in the case of polishing silicon wafers, a plurality of silicon wafers are adhered onto the carrier plate and pressed onto a polishing plate together with the carrier plate. The silicon wafers and the polishing plate are relatively moved to polish the silicon wafers. These days, flatness of the polished silicon wafers is very high, e.g., submicron order.
The polished silicon wafers are peeled from the carrier plate and conveyed to the next process; the carrier plate from which the silicon wafers have been peeled are cleaned and reused.
Therefore, the carrier plate is made of a material having high toughness and durability, e.g., ceramic.
Generally, the wafers are adhered onto the carrier plate by an adhesive, e.g., wax. The wax is dropped onto the wafer, then the wafer is spun so as to extend the wax, so that the whole surface of the wafer can be uniformly covered with the wax. Successively, the wafer is inverted and adhered onto the carrier plate, which has been preheated.
Surface condition of the surface of the cleaned carrier plate, on which the wafers are adhered, is partially minutely different. Namely, surface condition of one part, on which the wafer was adhered, is minutely different from that of another part, on which no wafer was adhered. For example, abrasive grains included in slurry, abraded dusts, etc. deposit on the part, on which no wafer was adhered, and said part is badly influenced by chemical substances included in the slurry.
On the other hand, no abrasive grains, etc. deposit on the part, on which the wafer was adhered, and said part is scarcely influenced by the chemical substances.
If the wafers are adhered onto the carrier plate without considering the minute differences of the surface of the carrier plate, some wafers bridge the two parts. If the wafer is accidentally adhered to bridge the two parts, the polishing work is badly influenced by the minute differences, so that the flatness of the polished wafer is made lower.
To solve the above described problem, a wafer adhering device capable of repeatedly adhering wafers at same places of a carrier plate was proposed (see Japanese Utility Model Gazette No. 2,562,044). The wafer adhering device is shown in FIG. 7.
In FIG. 7, the wafer adhering device 100 has an adhering table 102, which is capable of rotating in a direction xe2x80x9cAxe2x80x9d. A carrier plate 104 is mounted on the adhering table 102 and has marks 106. Sensors for detecting the marks 106 are provided. A sucking section 110 is vertically moved. A mounting unit mounts a wafer 108 held by the sucking section 110 on a prescribed position of an adhesion face 104a of the carrier plate 104.
In the wafer adhering device 100, firstly the carrier plate 104 is positioned on the basis of the positions of the marks 106 detected by the sensors, then the adhering table 102 is rotated until a prescribed position of the carrier plate 104, at which the wafer 108 was adhered for a previous adhering work, reaches a position under the sucking section 110. The rotation of the adhering table 102 is stopped when the prescribed position of the carrier plate 104, at which the wafer 108 was adhered for the previous adhering work, reaches the position under the sucking section 110. Then, the sucking section 110 is moved downward so as to mount the wafer 108 at the prescribed position, at which the wafer 108 was adhered for the previous adhering work.
Further, a method of periodically changing positions of adhering wafers in a carrier plate on the basis of detected marks was disclosed in Japanese Patent Gazette No. 11-320393.
In the method disclosed in the Japanese Patent Gazette, a whole surface of the carrier plate can be uniformly used to adhere the wafers, so that surface conditions of the carrier plate can be uniform and the wafers can be adhered under uniform condition.
In the device and method disclosed in said Japanese Gazettes, flatness of the abraded wafers can be improved. However, the position of the carrier plate is defined at the adhering table, on which the wafers are adhered. Required time for positioning the carrier plate is longer than that for adhering wafers onto the carrier plate, so that it takes a long time to position the carrier plate and adhere the wafers thereonto.
An object of the present invention is to provided a method capable of adhering a wafer to a prescribed position of the carrier plate, which has been correctly positioned, in a short time.
Another object is to provide a device for executing said method.
To shorten the time for adhering the wafers at an adhering table, the inventor proposed to separately execute the step of positioning the carrier plate and the step of mounting the wafers onto the carrier plate. Further, he proposed to position the carrier plate while the carrier plate is preheated.
Namely, the method of the present invention comprises the steps of:
heating a carrier plate;
detecting a mark provided to a predetermined position of the carrier plate rotating at predetermined rotational speed;
positioning the carrier plate on the basis of a position of the detected mark;
conveying the carrier plate to a wafer adhering section with keeping a posture of the carrier plate which has been positioned in the positioning step; and
adhering the wafer at a prescribed position of the carrier plate.
Further, the wafer adhering device of the present invention, which adheres a wafer heated at a heating section to a carrier plate, comprises:
means for detecting a mark provided to a predetermined position of the carrier plate rotating at predetermined rotational speed;
means for positioning the carrier plate on the basis of a position of the detected mark;
means for conveying the carrier plate to a wafer adhering section with keeping a posture of the carrier plate which has been positioned in the positioning step; and
means for mounting the wafer at a prescribed position of the carrier plate which has been conveyed to an adhering table.
In the present invention, positioning the carrier plate and mounting the wafer are separately executed, and positioning the carrier plate is executed in the step of heating the carrier plate, whose required time is shorter than other steps. Therefore, mounting the wafer, whose required time is shorter than that of positioning the carrier plate, can be executed at the adhering table. Unlike the conventional technology in which positioning the carrier plate and mounting the wafer are executed at the adhering table, the present invention is capable of shortening the required time of mounting the wafer. Therefore, time of a preparation step can be shortened, so that total time of abrading the wafer can be shortened.
In the present invention, the mark may be a wide mark, rotational speed of the carrier plate may be made slower than the predetermined rotational speed when one end of the mark is detected, and rotation of the carrier plate may be stopped when the other end of the mark is detected. In this case, movement of the carrier plate, which is occurred after the rotation of the carrier plate is stopped, can be prevent, so that positioning accuracy of the carrier plate can be improved.
Further, in the present invention, the mark may be detected by a sensor provided to a heating table for heating the carrier plate. In this case, the carrier plate can be correctly positioned easily.